Watermelon green mottle mosaic virus (WGMMV) is a recently described virus that was discovered in 2007 infecting commercial watermelon fields in Taiwan. It is a cucurbit-infecting tobamovirus with a genome size and organization similar to other viruses in that subgroup. In 2017 and 2018 WGMMV was discovered infecting several species of cucurbits in three counties in California. Each of the detections occurred on small farms (>20 acres) for in-state markets. To determine if there was a single introduction followed by intrastate movement, or multiple introductions, we completed high-throughput sequencing (HTS) on RNA derived from crude virion purifications of each isolate and compared the sequences. We also performed greenhouse host range studies and found that WGMMV has a wide cucurbit host range, can systemically infect Nicotiana benthamiana, and form local lesions on Chenopodium amaranticolor. Additionally, an epidemiolocially important feature of many tobamoviruses is seed transmissibility. To examine the seed transmissibility of WGMMV we produced seeds from infected cucumber in the greenhouse, then tested individual seeds for the presence of the virus with and without surface disinfestation treatment. Untreated and treated seeds used as inoculum caused systemic infections in healthy host plants. This indicates infectious virus is present on and within the seed coat, as previously described for Cucumber green mottle mosaic virus. Infected seeds were also grown and tested for systemic infection. These results indicate that WGMMV is seed transmissible.